JP2644839B2 - Network controller - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a network control device applied to a communication device such as a facsimile device connected to a telephone line.

2. Description of the Related Art In general, this type of network control unit (NCU) has a DC loop function for operating a switch at the time of connection, a low impedance (usually 600Ω) termination function adapted to line impedance, and a telephone line connected to a commercial power supply or a ground. Requires insulation / separation functions. A telephone line terminated with a low impedance is usually connected to a modulation / demodulation circuit in an AC manner.

In addition, a facsimile apparatus having an additional function such as automatic reception requires a function of detecting a tonal call signal in a facsimile network or the like and a tonal control signal from a telephone or the like with high impedance.

That is, it is necessary to set the input impedance of the facsimile apparatus to high impedance during facsimile standby, to low impedance during facsimile operation, and to detect and transmit signals.

FIG. 4 shows a conventional example of a network control device for realizing such a function.

In FIG. 4, 1 and 2 are line terminals to which a telephone line is connected, and 3 and 4 are telephone terminals to which a telephone is connected.
Reference numeral 5 denotes a relay controlled by a relay control signal 6 from a facsimile control circuit (not shown).
8 and 9 are contacts of the relay 5. Telephone terminals 3, 4
Is connected to line terminals 1 and 2 via relay contacts 7 and 8.

Reference numeral 10 denotes a line transformer. The terminals of the primary winding are connected to line terminals 1 and 2, and a relay contact 9 is inserted between the intermediate terminals. When the relay contact 9 is closed, the primary winding and the line terminals 1 and 2 are closed in a DC and AC manner, and at that time, a DC current necessary for the operation of the exchange flows by the line side power supply (a DC loop is connected). ), The DC impedance of the primary winding is set.

The secondary winding of the line transformer 10 is insulated and separated from the primary winding, and a modulation / demodulation circuit 11 is connected to the secondary winding. When the relay contact 9 is closed, the line terminals 1 and 2 and the modulation / demodulation circuit 11 are AC-coupled via the line transformer 10, and at that time a low impedance (normally 600Ω) that matches the line impedance.
Circuit terminals 1 and 2 so that
The input impedance of 1 and the turns ratio of the line transformer 10 are determined.

Now, in order to perform automatic reception, it is necessary to detect a call signal from a calling side (exchange) and connect a telephone line to a facsimile side. This ringing signal includes a ringer signal (usually 16) sent from the exchange for ringing the telephone bell.
Hz) and a facsimile-only ringing signal that does not ring the telephone (typically 1300 Hz).

Reference numeral 12 denotes a tonal signal detection circuit for detecting such a tonal signal, which is AC-coupled to the line terminals 1 and 2 via a transformer 13 and a capacitor 15. The capacitor 15 is inserted in order to prevent the primary winding of the transformer 13 from forming a DC loop. Further, the input impedance of the tonal signal detection circuit 12 and the turns ratio of the transformer 13 are determined so that the AC termination impedance of this circuit portion is increased.

 The 16 Hz detection circuit is omitted in the figure.

In the above configuration, since the relay control signal 6 is off during the facsimile standby state, the relay contacts 7, 8, and 9 are in the states shown in the figure respectively, the line is connected to the telephone, and the tonal signal detection circuit is AC-coupled. Combined with 12.

In this state, when receiving the facsimile-specific calling signal, the tonal signal detection circuit 12 turns on the detection signal 16. The facsimile control circuit (not shown) turns on the relay control signal 6 when the detection signal 16 is turned on, and turns the relay 5 on.
, The relay contacts 7 and 8 are opened, and the relay contact 9 is closed.

As a result, the telephone is disconnected from the line, but a DC loop is formed by the primary winding of the line transformer 10, and the line is AC-terminated with a low impedance by the modem circuit 11.

Thus, facsimile communication is enabled, and transmission data 17 from the facsimile control circuit is modulated and transmitted to the line, or a signal from the line is demodulated and transmitted to the facsimile control circuit as reception data 18.

However, according to such a configuration, a large-sized and expensive transformer (transformer) is required outside the line transformer for detecting a tonal signal as compared with other circuit components, and this requires a network controller or a network controller. There has been a problem that the size of the facsimile machine, the production cost, and the reliability decrease.

The present invention has been made in view of the above problems, and has as its object to provide a network control device in which the number of transformers is reduced without impairing the functions.

Means for Solving the Problems In order to achieve the above-mentioned object, the present invention provides a relay connected to an intermediate terminal of a primary winding of a line transformer and closing the primary winding and a line to DC during a communication operation. And a single capacitor and a resistor connected in parallel with the relay terminal to close the primary winding and the line to an alternating current, and to provide a terminating impedance of the line on the secondary side of the line transformer. Means for switching to low impedance during communication operation and high impedance during communication standby are provided, and a modulation / demodulation circuit and a tonal signal detection circuit are connected to the secondary winding of the line transformer.

According to the configuration described above, during communication standby, the line is AC-closed to the tonal signal detection circuit connected to the secondary winding of the line transformer due to the AC closing of the line and the primary winding of the line transformer. The tonal signal from the line can be detected by the tonal detection circuit because it is coupled and the line is terminated in an AC manner with high impedance.

On the other hand, during a communication operation, a DC loop is formed by a DC closing of the line on the primary side of the line transformer and the line, and the line is also AC-coupled to the secondary side of the line transformer and terminated with low impedance. You. Therefore, communication is possible via the modulation / demodulation circuit connected to the secondary winding of the line transformer.

Embodiment An embodiment of the present invention will be described below with reference to FIGS. In FIGS. 1 to 4, the same reference numerals indicate the same or equivalent parts.

FIG. 1 is a configuration diagram of a network control device according to a first embodiment of the present invention. In this embodiment, a transformer corresponding to the transformer 13 shown in FIG. 4 is omitted, the only transformer is the line transformer 10, and the tonal signal detection circuit 12 is connected to the secondary side of the line transformer 10. This configuration is the same in other embodiments described later.

In FIG. 1, a relay contact 9 is connected in series to the intermediate terminal of the primary winding of the line transformer 10 in the same manner as in the prior art. A capacitor 20 and a resistor 21 are connected in parallel to the relay contact 9. I have. The capacitor 21 is provided for closing the line and the primary winding of the line transformer 10 in an AC state when the relay contact 9 is open (that is, when a DC loop is not formed). is there. The resistor 21 is provided to limit the discharge current of the capacitor 20 flowing when the relay contact 9 is closed, and to protect the relay contact 9.

22 is one of the contacts of the relay 5, and this relay contact 22
Thus, the tonal signal detection circuit 12 is connected to the secondary winding of the line transformer 10 during facsimile standby, and the modem circuit 11 during facsimile operation.

Note that the input impedance of the tonal signal detection circuit 12 is set so that when it is connected to the line transformer 10, the line is terminated with a predetermined high impedance, and the input impedance of the modem circuit 11 is the same as that of the line transformer 10. The connection is set so that the line is terminated at a predetermined low impedance. Therefore, the relay contact 22
Depending on the modulation / demodulation circuit 11 or tonal signal detection circuit 12
, The AC terminal impedance of the line is also switched.

The operation of the network control device configured as described above will be described below.

During standby of the facsimile, since the relay control signal 6 from the facsimile control circuit (not shown) is off, the relay contacts 7, 8, 9, and 22 are in the state shown in the figure. The line is connected to the telephone via relay contacts 7,8. Also,
Since the relay contact 9 is open, no DC loop is formed.
It is closed with the 10 primary windings in terms of AC. The secondary winding of the line transformer 10 is connected to the tonal signal detection circuit 12 via the relay contact 22.

Therefore, in terms of AC, the line is coupled to the tonal signal detection circuit 12 via the line transformer 10 and terminated with high impedance. Therefore, the tonal signal detection circuit 12 detects a tonal signal (such as a facsimile start signal from a facsimile network) from the line, turns on the detection signal 16, and starts a facsimile operation by a facsimile control circuit (not shown). be able to.

On the other hand, during facsimile operation, the relay control signal 6 from the facsimile control circuit is turned on to drive the relay 5, so that the relay contacts 7, 8 are opened, the relay contact 9 is closed, and the relay contact 22 is directed to the modem circuit 11 side. Switch.

By closing the relay contact 9, the primary winding and the line of the line transformer 10 are closed in a DC manner (also in an AC manner), and a DC loop is formed. Also, in terms of AC, the modulation / demodulation circuit 11
, And is terminated at a low impedance via the line transformer 10. Thus, the transmission data 17 can be modulated and transmitted to the line, or the signal from the line can be demodulated to obtain the reception data 18.

FIG. 2 is a configuration diagram of a network control device according to a second embodiment of the present invention. In this embodiment, the modulation / demodulation circuit 11 and the tonal signal detection circuit 12 are directly connected to the secondary winding of the line transformer 10, and the modulation / demodulation circuit 11 is connected to the tonal signal detection circuit.
High impedance termination is used in the same way as 12.

Switching of the terminal impedance of the line is performed by connecting / disconnecting the low impedance terminal resistor 24 to / from the secondary winding of the line transformer 10 by a relay contact 23 which is one of the contacts of the relay 5.

In such a configuration, while the facsimile is on standby, the line and the secondary side of the line transformer 10 are AC-coupled by the action of the capacitor 20 as in the first embodiment,
Also, since the relay contact 23 is open, the line is terminated with high impedance. As a result, the facsimile start signal and the like from the line can be detected by the tonal detection circuit 12.

During facsimile operation, the relay contact 19 is closed to form a DC loop, and the relay contact 23 is closed and the terminating resistor 24 is connected to the secondary side of the line transformer 10, so that the line is terminated with low impedance. . Thus, facsimile communication can be performed via the modulation / demodulation circuit 11.

FIG. 3 is a configuration diagram of a network control device according to a third embodiment of the present invention. In the present embodiment, the switching of the termination impedance is the same as in the second embodiment, but the modulation / demodulation circuit 11 and the tonal detection circuit 12 (FIG. 2) are integrated into a high impedance signal processing circuit 26.

For the primary side of the line transformer 10, the intermediate terminal of the primary winding and its relay contact are omitted, and the DC loop control is performed by relay contacts 27 and 28 for switching the line connection to the telephone or the line transformer 10. It has been changed to be done. Also, the capacitor 20 and the resistor 21
A capacitor 30 and a resistor 31, and a capacitor 32 and a resistor 33, which have the same functions as those described above, are connected between the line terminals 1 and 2 and each terminal of the primary winding of the line transformer 10.

In the above configuration, when the facsimile is on standby, the relay contacts are in the state shown in the figure, and a DC loop is not formed.
It is coupled to the primary side of the line transformer 10 and terminated by the signal processing circuit 26 with high impedance. Therefore, the signal processing circuit 26 can detect a tonal signal such as a facsimile start signal from the line.

On the other hand, during the facsimile operation, the relay 5 is driven by the relay control signal 6, the relay contacts 27 and 28 are switched to the facsimile side, and a DC loop is formed by the primary winding of the line transformer 10. The line is terminated with low impedance by the terminating resistor 24. Thus,
The signal processing circuit 26 enables facsimile communication with the line via the line transformer 10.

The relay contacts in each embodiment need not necessarily be the contacts of the same relay, but may be the contacts of different relays.

Further, each embodiment is an example applied to a facsimile, but the present invention is also applicable to a network control device of a similar communication device connected to a telephone line.

As is apparent from the above description, the present invention relates to a relay connected in series to an intermediate terminal of a primary winding of a line transformer and closing the primary winding and a line to DC during a communication operation. And a single capacitor and a resistor connected in parallel with the relay terminal to close the primary winding and the line to an alternating current, and to provide a terminating impedance of the line on the secondary side of the line transformer. Conventionally, a configuration is provided in which a means for switching to low impedance during communication operation and high impedance during communication standby is provided, and a modulation / demodulation circuit and a tonal signal detection circuit are connected to the secondary winding of the line transformer. Since the number of transformers required for signal detection can be reduced by one to achieve the same function, the size and reliability of the network control device or communication device can be reduced. This has the effect of greatly contributing to a reduction in parts cost.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a network control device according to a first embodiment of the present invention, FIG. 2 is a configuration diagram of a network control device according to a second embodiment of the present invention, and FIG. FIG. 4 is a configuration diagram of a network control device according to an embodiment, and FIG. 4 is a configuration diagram of a conventional network control device. 1,2 ... line terminal, 3,4 ... phone terminal, 5 ... relay,
7,8,9,22,23,27,28 ... Relay contact, 10 ... Line transformer, 11 ... Modulation / demodulation circuit, 12 ... Tonal signal detection circuit, 20,30,32 ... Capacitor, 24 ... Terminating resistor, 26 ……
Signal processing circuit.

 ──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A 1-254057 (JP, A) JP-A 64-55953 (JP, A) JP-A 62-142454 (JP, A)

Claims (1)

(57) [Claims] A relay terminal connected in series to an intermediate terminal of a primary winding of a line transformer for closing the primary winding and a line to DC during a communication operation, and a relay terminal connected in parallel to the relay terminal. A single capacitor and a resistor for closing the primary winding and the line to an alternating current, and a secondary winding of the line transformer, the terminal impedance of the line is set to a low impedance during the communication operation, and the communication is standby. Having switching means for switching to high impedance inside,
A network controller, wherein a modulation / demodulation circuit and a tonal signal detection circuit are connected to a secondary winding of the line transformer.